Gas turbine engines are an efficient source of energy and have proven useful to propel aircraft and other flying machines, for electricity generation, as well as for other uses. One aspect of gas turbine engines is that they produce significant amounts of thermal energy during operation. It is well understood that some thermal energy is harnessed by a gas turbine engine during its operation; however, a significant amount of thermal energy is not harnessed or put to use and is lost. Thus, there remains a need for systems, apparatuses, and methods of harnessing thermal energy of gas turbine engine(s).